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Posted: **Fri Jun 21, 2024 6:33 pm**

Hi,

I am trying to apply a master to slave nodes relationship between a single node (master) and many nodes at the same elevation level (slave) of continuum 8-node SSPbrickUP elements. I am aware of the EqualDOF command and the RigidLink command that might help with this. However, the information in the OpenSees manual does not provide a clear difference between these two commands.

I would like to ask, what is the difference between these two commands?

Also, if I set EqualDOF between master and slave nodes in the 1, 2, 3 (x, y, z) directions, is it equivalent to setting a RigidLink bar ($type) command?

Thanks for your your explanation and advice in advance.
Sincerely,
Ryan Chia

Posted: **Mon Jun 24, 2024 1:53 pm**

Yes, both are same. Both equalDOF and rigidLink construct multi-point constraints object. equalDOF constrains specific DOFs to be equal, while rigidLink constrains all DOFs to move together as a rigid body. Please note that RigidLink 'beam' type couples translations and rotations, while 'bar' type only constrains translations. If you want to see the constraint matrix, type the following OpenSees commands on the OpenSees interpreter.

Code: Select all

# Sets the dimension
model basic -ndm 3 -ndf 6

# Nodes definition
node 1 0 0 0
node 2 1 0 0
node 3 2 0 0
node 4 3 0 0

# Create constraint object
constraints Plain

# Apply equalDOF constraint between 1 (retained) and 2 (constrained) node on DOFs 1 2 3
equalDOF 1 2 1 2 3

# Apply rigidLink with bar option on 3 (master) and 4 (slave)
rigidLink bar 3 4

# Prints the entire model
printModel

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